That quote irritates the crap out of me. I read it and think "Well, bravo and good for you, Dubs! Let me slow clap while you sashay your butt out of the room." (I realize that he passed in 1965, but you get the gist.)
We are told that as writers we must write every day, regardless. And I get it. You will never play the cello like Yo-Yo Ma or paint like Pablo Picasso, if you don't practice.
Speaking of Picasso, I found an inspirational quote of his, that I feel is more helpful: Inspiration does exist. But it must find you working.
People who get writer's block are jerks*
*W. Somerset Maugham never said this ... probably